Method and device for filtering a signal

ABSTRACT

A method and a device are described for filtering a variable. A first filtering arrangement is used for forming an output variable as a function of an input variable, the first filtering arrangement having at least a delaying effect. The input variable of the first filtering arrangement is corrected using a correcting variable which is obtained by starting from the input variable of the first filtering arrangement and by filtering, using a second filtering arrangement.

FIELD OF THE INVENTION

The present invention relates to a method and a device for filtering asignal.

BACKGROUND INFORMATION

A method and a device for filtering a signal are referred to, forexample, in the German Published Patent Application No. 195 37 787. Adriver input amount may be filtered using a control signal-formingelement. The filtering may be configured so that, for example, rapiddriver input quantity changes (pedal force) may not act undamped on thefuel metering, and thus initiation of longitudinal vibrations of thevehicle may be avoided. Such filtering for the damping of the activationof systems may, in response to ramp-like changes in the input variable,generate a lag error. Therefore, the output variable may follow theinput variable only at a delay. In an internal combustion engineapplication, for example, this may have the effect of a diminished drivetorque.

SUMMARY OF THE INVENTION

According to an exemplary embodiment and/or exemplary method of thepresent invention, respective lag errors may be compensated for withoutlimitations of the filtering effect having to be accepted, particularlyin the case of stepwise changes in the input variable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fundamental construction of a fuel metering system.

FIG. 2 shows a block diagram of an exemplary method according to thepresent invention.

DETAILED DESCRIPTION

The present invention is described below, using the example of a fuelquantity signal in a self-igniting internal combustion engine. However,the present invention is not limited to this application. It may also beused in the case of other signals, such as, for example, in the case ofsignals which are used for the control of internal combustion engines.In particular, the exemplary method may be suitable for signals whichinfluence or characterize the output torque. Such signals may be, forexample, a fuel quantity signal, signals controlling power-influencingactuators, a quantity input signal, the output signal of an acceleratorpedal sensor or a engine speed signal.

FIG. 1 shows a fundamental construction of a fuel metering system of aninternal combustion system. Number 10 denotes an accelerator positionsensor and 11 denotes a speed sensor. A setpoint value control 12 isconnected to the accelerator-pedal position sensor and speed sensor 11.Output signal MEW of the setpoint control, which corresponds to thedriver input quantity, goes to a control signal-forming element 13.Engine speed signal N of engine speed sensor 11 goes to a disturbancevariable regulator 14. Output signal MEF of control signal-formingelement 13 and output signal MES of disturbance variable regulator 14are superimposed in a summing point, and form quantity signal MEA whichis fed to a setting element 15. As a function of this signal MEA, acorresponding amount of fuel is metered to the internal combustionengine (not shown).

Starting from the accelerator position and the engine speed, setpointvalue control 12 computes driver input quantity MEW which is requiredfor making available the driving power input by the driver. In systemswithout anti-surge control, this signal is conducted directly to settingelement 15. Setting element 15 converts this signal to a control signalfor application to the corresponding actuators. Thus, for example, inthe case of in-line fuel injection pumps, it may be provided that asetting regulating circuit adjusts the control rod positions to anappropriate value. In time-controlled systems, setting element 15 emitsa control signal for a quantity-determining magnetic valve or a piezoactuator.

To compensate for judder vibrations when they occur, driver input signalMEW may be filtered using a control signal-forming element 13. Controlsignal-forming element 13 has a delaying effect. Thus, for example,filters having PT1 properties may be used. It may be desirable if, ascontrol signal-forming element, filters are used which include furthercomponents.

Furthermore, engine speed signal N is conducted to a fault regulator 14.The new mode of operation of this device is discussed in GermanPublished Patent Application No. 195 37 787.

If filter 13, which forms the control signal-forming element, has atleast delaying behavior, such as a T1 element, a lag error may appear inresponse to certain changes in the input variable of filter 13.Therefore, the output variable follows the input variable only at adelay.

According to an exemplary embodiment and/or exemplary method of thepresent invention, this lag error may be rectified by applying to theinput of the filter a correction value formed from the input variable.For example, for this purpose, the input variable may be derived withrespect to time, i.e. differentiated, and subsequently weighted with apredefinable value. This weighting factor may be predefined as afunction of the response characteristic of the filter to be corrected.In this context, the derivation with respect to time of the inputvariable is limited, in order to maintain the filtering effect, inresponse to the rapidly changing input variable, in spite of themeasures against lag errors.

In FIG. 2 the control signal-forming element having such a correction isshown in greater detail. Elements which have already been described inFIG. 1 are denoted by corresponding reference symbols.

The actual filter of the control signal-forming element is denoted asfirst filter 100. Input variable MEW of control signal-forming element13, on the one hand, having a positive sign, reaches a linkage point125, and on the other hand, it reaches a second filter 110. The outputsignal of linkage point 125 reaches first filter 100.

The output signal of second filter 110, via a limiter circuit, reaches asecond linkage point 115. The output signal of linkage point 115, havinga positive sign, reaches linkage point 125. The output signal of afactor input 120 forms the second input of second linkage point 115. Theoutput signal of first filter 100 forms the output variable MEF.

In one exemplary embodiment it may also be provided that limiter circuit112 is positioned after linkage point 115. This means that limitercircuit 112 limits the correcting variable by which the input variableof first filter 100 is corrected in linkage point 125.

A further exemplary embodiment according to the present invention isshown by dots and dashes. Here, the input variable, via an amplifier140, additionally reaches a linkage point 130, at whose second input theoutput variable of first filter 100 is present. Then, these two linkedvariables form output variable MEF.

Second filter 110 may be configured as a differentiator. Second filter110 includes at least one differentiating component. For example, thesecond filter may also have a PD element or be configured as a DTelement. The output variable of second filter 110 is limited by limitercircuit 112 to the highest admissible values, in absolute value terms,so as to ensure the filter effect in response to a rapid, and, forexample, stepwise change of input variable MEW.

Limiter circuit 112 is dimensioned so that the limitation in response toa slowly changing input value is ineffective, and filter 110 delivers anuninfluenced contribution to the correction of the input variable offirst filter 100. In response to slow changes of the input variable,second filter 120 has a relatively large influence on the filteredvariable. According to an exemplary embodiment and/or exemplary methodthe present invention, this may prevent the lag errors. In the case ofstepwise, that is, rapid changes of the input variable, the limitationmay be effective, whereby the corresponding contribution of secondfilter 110 to the correction of the input variable of the first filteris only small. In response to slow changes of the input variable, secondfilter 120 has a relatively small influence on the filtered variable. Inthis case, first filter 100 may have a great influence on the filteredvariable.

In linkage point 115, the output signal of second filter 110 is weightedwith a preset weighting factor from factor input 120. The weightingfactor is to be preset as a function of the response characteristic offirst filter 100.

In one exemplary embodiment, first filter 100 has the response functionK/(T*s+1)

Here the value T is denoted as the time delay constant and the value Kas the proportional gain.

The factor of factor input 120 may be identical to time constant T. Thismeans that the output signal of second filter 110, limited by limitercircuit 112, is weighted with the factor of factor input 120, i.e. withtime delay constant T of first filter 100.

In a second exemplary configuration, amplifier 140 has a gain V. Theproportional gain K of the first filter then takes on the value K=1−V.

According to an exemplary embodiment and/or exemplary method of thepresent invention, input variable MEW of first filter 100 is correctedas a function of a correcting variable. This means that, starting frominput variable MEW of the first filter, the correcting variable for thecorrection of this input variable is determined. In one exemplaryembodiment, the input variable is derived with respect to time ordifferentiated, and is thereafter weighted with a factor. In thiscontext, the factor may be determined by the response characteristic ofthe first filter. The factor corresponds to the time delay constant T ofthe first filter.

A part of the signal may be corrected. This may be implemented in thatthe proportional gain K of the first filter is selected as less than 1,and a correspondingly amplified input signal is fed to the output signalof the first filter.

1. A device for filtering a variable, comprising: a first filteringarrangement for forming a first output variable as a function of aninput variable and a correcting variable which are fed to at least thefirst filtering arrangement, the first filtering arrangement having adelaying effect; and a second filtering arrangement for receiving theinput variable and generating an intermediate output variable byfiltering the input variable, wherein the correcting variable isgenerated by the second filtering arrangement by weighting theintermediate output variable with a predetermined weighting factor. 2.The device of claim 1, wherein the second filtering arrangement includesa differentiating property.
 3. The device of claim 1, wherein theintermediate output variable of the second filtering arrangement islimited by a limiter unit of the second filtering arrangement.
 4. Thedevice of claim 1, wherein the weighting factor is determined as afunction of a response characteristic of the first filteringarrangement.
 5. A method for filtering a variable, comprising:generating a first output variable using a first filtering arrangement,as a function of an input variable and a correcting variable which arefed to at least the first filtering arrangement, wherein the firstfiltering arrangement has a delaying effect; generating an intermediateoutput variable using a second filtering arrangement, wherein the secondfiltering arrangement receives the input variable and generates theintermediate output variable by filtering the input variable; andgenerating the correcting variable using the second filteringarrangement, by weighting the intermediate output variable with apredetermined weighting factor.